turns out david petraeus was not the original focus of an fbi investigation. nbc's andrea michelle first broke the story. she says she has more on the fbi's in -- how the fbi inadvertently found out about the general's affair. >> general david petraeus tumbled from the highest levels of government service after acknowledging what he called unacceptable behavior. an extramarital affair exposed bay cascading series of events that sources say started with a seemingly unrelated complaint to the fbi. triggered by e-mails from petraeus's biography paula broadwell to another woman not related to petraeus who felt she was being harassed and complained to the fbi. officials say in recent weeks, the fbi traced the e-mails to broadwell and only stumbled on the relationship with petraeus as a result. >> it's so politically sensitive that my guess is the decision was made near or at the top level of the fbi to sit down with general petraeus and have a discussion with him and let him know that this information had been discovered. >> broadwell has not been shy about her acc